Eddy current flaw detection device

Abstract

To provide an eddy current flaw detection device that removes noise signals generated by vibration of the eddy current flaw detection device and eccentricity or vibration of a body to be inspected.SOLUTION: An eddy current flaw detection device is provided with a pair of detection coils 10a, 10b that is arranged coaxially with and separated from a body to be inspected 3, and a bridge circuit in which two sides of a bridge are formed of the detection coils so that magnetic fields generated by the detection coils 10a, 10b have opposite phases. A first exciting coil 11 and a second exciting coil 12 are arranged coaxially with the pair of detection coils 10a, 10b to sandwich the detection coils 10a, 10b. A distance D between the detection coils 10a, 10b and the second exciting coil 12 arranged adjacent thereto is set to a distance at which vibration noise signals detected by the detection coils 10a, 10b excited by and adjacent to the second exciting coil 12 and vibration noise signals detected by the detection coils 10a, 10b excited by the first exciting coil 11 have opposite phases.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an eddy current inspection device, and more particularly to a mutual induction type eddy current inspection device that includes an excitation coil that generates an excitation magnetic field to generate eddy currents in a surface layer of an object to be inspected, a pair of differentially connected detection coils, and a signal processing unit that processes signals resulting from impedance changes of the detection coils, and inspects defects and the like of the object to be inspected based on the signals. [Background technology]

[0002] Eddy current testing equipment is used as a surface inspection technique to detect the presence or absence of defects such as scratches by inducing eddy currents on the surface of the test object and detecting the change in the reaction magnetic field created by this eddy current. Eddy current testing equipment is classified into a self-comparison type, in which the excitation coil and detection coil are configured as a single coil, and a mutual induction type, in which each is configured as a separate coil. It is desirable to improve the signal-to-noise ratio of these eddy current testing equipment.

[0003] For example, Patent Document 1 discloses an eddy current flaw detection device in which a pair of detection coils are arranged coaxially and non-contact with a conductor being inspected, a pair of resonant coils are arranged coaxially with the detection coils so that the magnetic fields generated between the pair of detection coils are in phase with each other, and a capacitance circuit is provided in the resonant coil.

[0004] In the eddy current flaw detector described in the above-mentioned Patent Document 1, if there is no flaw or foreign object inside the conductor, the induced current flowing through the resonant coil is offset, so there is no change. In contrast, in the above-mentioned device, if there is a flaw or foreign object inside the conductor, a bias occurs in the magnetic field generated by each detection coil, so that a difference occurs in the induced current value generated by each resonant coil, and this difference in current flows, causing the resonant coil to resonate. As a result, the above-mentioned device can improve the S / N ratio. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 2882856 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above-mentioned Patent Document 1, when a noise signal is generated due to vibration of the eddy current flaw detector or eccentricity or vibration of the test object, the S / N ratio decreases due to the noise signal.

[0007] Furthermore, in the above-mentioned Patent Document 1, an amplifier circuit for amplifying the output of each resonance coil is required, which makes the device complicated.

[0008] An object of the present invention is to provide an eddy current flaw detector capable of eliminating noise signals due to vibration of the inspection device and eccentricity or vibration of the object to be inspected without complicating the device. [Means for solving the problem]

[0009] The present invention provides an eddy current flaw detection device comprising a pair of detection coils arranged coaxially and spaced apart from each other in a non-contact manner with respect to an object to be inspected, and a bridge circuit in which the detection coils form two sides of a bridge so that the magnetic fields generated by these detection coils are in opposite phase, the device comprising a first excitation coil that generates an excitation magnetic field to generate eddy currents in a surface layer portion of the object to be inspected, and a second excitation coil that generates an excitation magnetic field to generate eddy currents in a surface layer portion of the object to be inspected, the second excitation coil being composed of a pair of coil portions arranged coaxially with the detection coils so as to sandwich the pair of detection coils, the second excitation coil generating an excitation magnetic field to generate eddy currents in the surface layer portion of the object to be inspected, the distance between the detection coil and the coil portion of the second excitation coil arranged adjacent to it is set to a distance at which the phase of a noise signal due to eccentricity or vibration excited by the second excitation coil and detected by the adjacent detection coil changes, and a noise signal due to eccentricity or vibration excited by the first excitation coil and detected by the detection coil changes.

[0010] By configuring the present invention as described above, it is possible to change the phase of a noise signal due to vibration of the inspection device obtained from the excitation magnetic field by the first excitation coil and eccentricity or vibration of the object under test, and a noise signal due to vibration of the inspection device obtained from the excitation magnetic field by the second excitation coil and eccentricity or vibration of the object under test. As a result, the noise signals are superimposed on each other, making it possible to reduce the noise signals and improving the S / N ratio.

[0011] In addition, the present invention can be configured such that the first excitation coil is composed of a pair of coil sections arranged coaxially with each of the pair of detection coils so as to sandwich the pair of detection coils, and the coil sections of the first excitation coil are arranged between the detection coil and each coil section of the second excitation coil.

[0012] Furthermore, in the present invention, the first excitation coil can be arranged concentrically with the detection coil and on the outer circumferential side of the detection coil.

[0013] Furthermore, in the present invention, it is preferable to set the distance between the detection coil and the second excitation coil arranged adjacent to it so that a noise signal due to eccentricity or vibration excited by the second excitation coil and detected by the adjacent detection coil has an opposite phase to a noise signal due to eccentricity or vibration excited by the first excitation coil and detected by the detection coil.

[0014] By configuring the present invention as described above, a noise signal due to vibration of the inspection device or eccentricity or vibration of the object under test obtained from the excitation magnetic field by the first excitation coil and a noise signal due to vibration of the inspection device or eccentricity or vibration of the object under test obtained from the excitation magnetic field by the second excitation coil are in opposite phase. As a result, the noise signals are superimposed on each other, making it possible to cancel out the noise signals and improving the S / N ratio.

[0015] Furthermore, the present invention is preferably configured such that AC power is supplied to the second excitation coil, and the phase of the AC power supplied to the second excitation coil is converted so that a noise signal due to eccentricity or vibration that is excited by the second excitation coil and detected by the detection coil located adjacent to the second excitation coil and a noise signal due to eccentricity or vibration that is excited by the first excitation coil and detected by the detection coil are in opposite phase to each other.

[0016] As described above, the present invention is configured to convert the phase of the AC power to be provided to the second excitation coil, so that a noise signal due to the vibration of the inspection device or the eccentricity or vibration of the object to be inspected, which is obtained from the excitation magnetic field by the first excitation coil, and a noise signal due to the vibration of the inspection device or the eccentricity or vibration of the object to be inspected, which is obtained from the excitation magnetic field by the second excitation coil, are in opposite phase to each other. As a result, the noise signals are superimposed on each other, making it possible to cancel each other out, improving the S / N ratio.

[0017] The present invention also provides a power amplifier for a synchronous rectifier including an oscillator, a first power amplifier for amplifying an AC output from the oscillator, a second excitation phase converter for converting a phase of the AC output from the oscillator, and a second power amplifier for amplifying the AC output from the second excitation phase converter, No. 1 AC power is applied from a power amplifier to the second excitation coil. Second It may be arranged to provide AC power from a power amplifier.

[0018] The object to be inspected is a metal round bar material or a metal round pipe material, the detection coil, the first excitation coil, and the second excitation coil are through coils, and Made of metal Round bar material Or the above-mentioned metal round pipe material The distance between the detection coil and the second excitation coil may be set based on the difference between the outer diameter of the detection coil and the inner diameter of the detection coil and the second excitation coil.

[0019] In addition, the present invention can be configured such that the object to be inspected is a metallic round pipe material or a metallic round bar material, and the eddy current inspection probe is arranged in close proximity to the object to be inspected and has the detection coil, the first excitation coil and the second excitation coil, and the eddy current inspection probe is formed in a cylindrical or semi-cylindrical shape.

[0020] In addition, the present invention provides a method for manufacturing a test piece, the test piece being a metal square pipe material or a metal square bar material, Test subject and an eddy current inspection probe having the detection coil, the first excitation coil, and the second excitation coil, the eddy current inspection probe comprising: The above The test piece may be configured to have a rectangular pipe shape formed so as to surround the test piece, or a rectangular plate shape arranged at a distance from the surface of the test piece. Effect of the Invention

[0021] According to the present invention, it is possible to provide an eddy current flaw detector capable of removing noise signals caused by vibration of the inspection device and eccentricity or vibration of the object to be inspected, thereby improving the S / N ratio. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic diagram of an eddy current flaw detector and an object to be inspected according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic circuit diagram showing the configuration of the eddy current flaw detector according to the first embodiment of the present invention. [Diagram 3] FIG. 3 is a block diagram showing an eddy current flaw detector according to the first embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram for explaining the removal of noise signals due to vibration of the eddy current flaw detector according to the present invention and eccentricity or vibration of the test object. [Diagram 5] FIG. 5 is a schematic diagram of an eddy current flaw detector and an object to be inspected according to the second embodiment of the present invention. [Figure 6] FIG. 6 is a schematic circuit diagram showing the configuration of an eddy current flaw detector according to the second embodiment of the present invention. [Figure 7] FIG. 7 is a block diagram showing an eddy current flaw detector according to the second embodiment of the present invention. [Figure 8] FIG. 8 is a block diagram showing an eddy current flaw detector according to the third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Next, an eddy current inspection device according to an embodiment of the present invention will be specifically described with reference to the attached drawings. Note that the eddy current inspection device according to the present invention is not limited to the embodiment shown below, and can be appropriately modified and implemented within the scope of the present invention.

[0024] As shown in Fig. 1, the object to be inspected 3 of the present invention is a conductor such as a round metal pipe or a round metal bar. An eddy current inspection probe 1 is placed close to the object to be inspected 3, and a flaw inspection is performed by detecting a change in an eddy current generated in the object to be inspected 3. The eddy current inspection probe 1 detects flaws, thinning, etc. of the object to be inspected 3 by eddy current inspection. In the following, flaws, thinning, etc. are collectively referred to as defects.

[0025] The eddy current inspection probe 1 used in the eddy current inspection device according to the first embodiment of the present invention is formed in a cylindrical or semi-cylindrical shape, and includes a pair of detection coils 10a, 10b, a first excitation coil 11 that generates an excitation magnetic field to generate an eddy current in the surface layer of the inspection object 3, and a second excitation coil 12. The second excitation coil 12 is composed of a pair of coil parts 12a, 12b that are arranged coaxially with the detection coils 10a, 10b so as to sandwich the pair of detection coils 10a, 10b. The eddy current inspection probe 1 according to the first embodiment of the present invention is a probe used in a mutual induction type eddy current inspection device. The first excitation coil 11 is used as a mutual induction excitation coil. The second excitation coil 12 is used as a noise cancellation excitation coil.

[0026] In the first embodiment, the pair of detection coils 10a, 10b, the first excitation coil 11, and the second excitation coil 12 are configured as through coils.

[0027] The first excitation coil 11 is composed of a pair of coil portions 11a and 11b arranged coaxially so as to sandwich the pair of detection coils 10a and 10b. The coil portion 11a of the first excitation coil 11 is arranged between the detection coil 10a and the coil portion 12a of the second excitation coil 12, and the coil portion 11b of the first excitation coil 11 is arranged between the detection coil 10b and the coil portion 12b of the second excitation coil 12.

[0028] By applying an alternating current to the pair of coil portions 11a, 11b constituting the first excitation coil 11 and generating an excitation magnetic field, an eddy current is generated in the surface layer portion of the inspection object 3. By applying an alternating current to the pair of coil portions 12a, 12b constituting the second excitation coil 12 and generating an excitation magnetic field, an eddy current is generated in the surface layer portion of the inspection object 3.

[0029] The pair of detection coils 10a, 10b are differentially connected. The pair of differentially connected detection coils 10a, 10b are connected to a bridge circuit. The pair of detection coils 10a, 10b detect changes in eddy currents generated in the object under inspection 3. When the voltages generated in the pair of detection coils 10a, 10b differ from each other, a signal indicating that a defect has been detected is output from the bridge circuit.

[0030] The detection coils 10a, 10b, the pair of coil portions 11a, 11b constituting the first excitation coil 11, and the pair of coil portions 12a, 12b constituting the second excitation coil 12 are arranged coaxially spaced apart and in non-contact with the object to be inspected 3. The eddy current flaw detection probe 1 and the object to be inspected 3 move relatively. That is, in the eddy current flaw detection device 100, the eddy current flaw detection probe 1 moves relative to the object to be inspected 3 to inspect the object to be inspected 3, and the object to be inspected 3 moves relative to the fixed eddy current flaw detection probe 1. In the eddy current flaw detection device 100 of this embodiment, the eddy current flaw detection probe 1 moves relative to the object to be inspected 3 in the direction of the arrow in the figure, inspects the condition of the surface of the object to be inspected 3, and detects the presence or absence of defects.

[0031] In this embodiment, the object to be inspected 3 is a metallic round pipe material or a metallic round bar material.

[0032] In this embodiment, the detection coils 10a, 10b and the coil portions 12a, 12b of the second excitation coil 12 disposed adjacent thereto are disposed at a distance D. As shown in Fig. 1, the coil portion 12a of the second excitation coil 12 and the detection coil 10a are disposed at a distance D from each other, and the coil portion 12b of the second excitation coil 12 and the detection coil 10b are disposed at a distance D from each other. This distance D will be described later.

[0033] Next, an outline of the circuit configuration of this embodiment will be described with reference to Fig. 2. Fig. 2 is a schematic circuit diagram showing the configuration of the detection coil portion of the eddy current flaw detector according to the present invention.

[0034] As shown in FIG. 2, the bridge circuit 24 is composed of detection coils 10a, 10b and resistors 13a, 13b. The detection coils 10a, 10b are connected as two sides of the bridge circuit 24, and the resistors 13a, 13b are connected as the other two sides of the bridge circuit 24.

[0035] A first excitation coil 11 composed of a pair of coil portions 11a, 11b is provided so as to sandwich the detection coils 10a, 10b. This embodiment is a mutual induction type eddy current flaw detector in which excitation is performed by the first excitation coil 11 and detection is performed by the detection coils 10a, 10b.

[0036] A mutual induction type eddy current flaw detector can increase the excitation voltage applied by the excitation coil. In other words, in a self-induction type, the size of the coil is restricted due to the relationship with the bridge circuit. In contrast, in a mutual induction type, there is no such restriction, so there is freedom in the size of the coil and it is easy to increase the excitation voltage. By increasing the excitation voltage, the detection signal can be increased. For example, when the clearance between the detection coil and the object being inspected is large, i.e., when the charging rate is low, the detection signal can be increased by increasing the excitation voltage, thereby improving the detection accuracy.

[0037] An AC output from an AC power supply 30 (oscillator 21 and first power amplifier 22 in FIG. 3) is applied to coil portions 11a and 11b of the first excitation coil 11, and the coil portions 11a and 11b are excited. The excitation from the coil portions 11a and 11b excites the surface layer of the object under test 3, and an eddy current is generated. The detection coils 10a and 10b detect the impedance change accompanying the change in magnetic flux generated by the eddy current with a detection portion 31 (phase detector 27, etc. in FIG. 3).

[0038] The detection coils 10a and 10b are differentially connected so that the magnetic fields they generate are in opposite phase to each other. In this embodiment, the first excitation coil 11 excites the test object 3, and the detection coils 10a and 10b detect a change in impedance accompanying a change in magnetic flux generated by an eddy current.

[0039] As shown in Fig. 2, a second excitation coil 12 consisting of a pair of coil portions 12a, 12b is provided so as to sandwich the detection coils 10a, 10b. An AC output from an AC power source 30 (an oscillator 21 and a second power amplifier 23 in Fig. 3) is provided to the coil portions 12a, 12b constituting the second excitation coil 12, and the coil portions 12a, 12b are excited. The excitation from the coil portions 12a, 12b magnetizes the surface layer of the test object 3, generating an eddy current. This second excitation coil 12 is used as a noise cancellation excitation coil.

[0040] The coil portion 12a is wound so that the magnetic field it generates is in phase with the coil portion 11a of the first excitation coil 11. The coil portion 12b is wound so that the magnetic field it generates is in phase with the coil portion 11b of the first excitation coil 11.

[0041] The detection coil 10a also detects a change in impedance that accompanies a change in magnetic flux generated by the coil portion 12a due to an eddy current from the object under test 3.

[0042] The detection coil 10b also detects a change in impedance that accompanies a change in magnetic flux generated by the coil portion 12b due to an eddy current from the object under test 3.

[0043] In this way, the detection coil 10a detects a change in the synthetic impedance based on the excitation of the coil portion 11a of the first excitation coil 11 and the excitation of the coil portion 12a of the second excitation coil 12. The detection coil 10b detects a change in the synthetic impedance based on the excitation of the coil portion 11b of the first excitation coil 11 and the excitation of the coil portion 12b of the second excitation coil 12. When there is no abnormality in the test subject 3, the output signal of this bridge circuit 24 is set to be zero-balanced.

[0044] An output between terminals A and B in FIG. 2 is output from detection section 31, and inspection of object 3 can be performed based on this output signal.

[0045] Next, the eddy current flaw detector according to the first embodiment of the present invention will be further described with reference to the block diagram of FIG.

[0046] As shown in FIG. 3, the eddy current flaw detector 100 includes an oscillator 21, a first power amplifier 22, a second power amplifier 23, a bridge circuit 24, a detection phase converter 26, an amplifier 25, and a phase detector 27.

[0047] As shown in FIG. 2, the bridge circuit 24 is composed of the detection coils 10a, 10b and resistors 13a, 13b of the eddy current flaw detection probe 1.

[0048] The AC output from the oscillator 21 is amplified by a first power amplifier 22 and is provided to the coil section (mutual induction excitation coil section) 11a, 11b of the first excitation coil 11. The AC output from the oscillator 21 is amplified by a second power amplifier 23 and is provided to the coil section (noise cancellation coil section) 12a, 12b of the second excitation coil 12.

[0049] The object under test 3 is excited by AC outputs applied to the coil portion 11a of the first excitation coil 11, the coil portion 12a of the second excitation coil 12, the coil portion 11b of the first excitation coil 11, and the coil portion 12b of the second excitation coil 12. Then, the detection coils 10a and 10b detect impedance changes accompanying changes in magnetic flux generated by eddy currents.

[0050] An unbalanced output between the detection coils 10a, 10b output from the bridge circuit 24 is amplified by an amplifier 25 and sent to a phase detector 27. An AC output from the oscillator 21 is applied to a detection phase converter 26. An output of the detection phase converter 26 is applied to the phase detector 27.

[0051] The detection phase converter 26 converts the signal from the oscillator 21 into a signal having the same phase as the excitation signal and a signal having a phase shift of 90 degrees with respect to the excitation signal, and supplies the converted signal to a phase detector 27 .

[0052] The unbalanced output amplified by the amplifier 25 and the output of the detection phase converter 26 are applied to a phase detector 27, and the outputs of the detection coils 10a, 10b are detected together with the output of the detection phase converter 26.

[0053] The phase detector 27 synchronously detects the unbalanced output using a signal of the same phase as the excitation signal to output an X-axis eddy current signal, and also synchronously detects the unbalanced output using a signal that is 90 degrees out of phase with the excitation signal to output a Y-axis eddy current signal. The detected X-axis and Y-axis eddy current signals are then input into a signal processing device 28 via a filter (not shown) and an A / D converter (not shown), and the measurement results and the like are displayed on an output unit 29 such as a display. The signal processing device 28 is, for example, configured as a personal computer (PC) connected to the eddy current flaw detector 100.

[0054] In this embodiment, damage or the like of the object under test 3 is detected based on the output values ​​from the detection coils 10a and 10b.

[0055] In the above-mentioned eddy current flaw detection device 100, when vibration of the eddy current flaw detection probe 1 or the object under test 3 or eccentricity between the eddy current flaw detection probe 1 and the object under test 3 occurs, the distance between the detection coils 10a, 10b and the object under test 3, and the distance between the first excitation coil 11 (coil portions 11a, 11b) and the second excitation coil 12 (coil portions 12a, 12b) and the object under test 3 each change, generating a noise signal.

[0056] When the eddy current inspection probe 1 moves, the movement of the eddy current inspection probe 1 generates vibrations in the eddy current inspection probe 1, which changes the distance between the detection coils 10a, 10b and the object 3 and the distance between the first excitation coil 11 (coil parts 11a, 11b) and the second excitation coil 12 (coil parts 12a, 12b) and the object 3, respectively, generating noise signals. When the object 3 moves, the movement of the object 3 generates vibrations in the object 3, which changes the distance between the detection coils 10a, 10b and the object 3 and the distance between the first excitation coil 11 (coil parts 11a, 11b) and the second excitation coil 12 (coil parts 12a, 12b) and the object 3, respectively, generating noise signals. Furthermore, even when the eddy current flaw detection probe 1 or the object under test 3 does not vibrate, if there is eccentricity between the detection coils 10a, 10b and the object under test 3 or between the first excitation coil 11 (coil portions 11a, 11b), the second excitation coil 12 (coil portions 12a, 12b) and the object under test 3, the distance between the detection coils 10a, 10b and the object under test 3 and the distance between the first excitation coil 11 (coil portions 11a, 11b), the second excitation coil 12 (coil portions 12a, 12b) and the object under test 3 will change, and a noise signal will be generated.

[0057] For this reason, in this specification, noise signals due to eccentricity or vibration refer to noise signals generated by changes in the relative distance between the detection coils 10a, 10b and the object under test 3 due to vibration of the coil or object under test or eccentricity of the coil or object under test.

[0058] Here, the inventors have thoroughly studied the relationship between the noise signal and the distance D between the detection coil 10a and the coil portion 12a of the second excitation coil 12 and the distance D between the detection coil 10b and the coil portion 12b of the second excitation coil 12. As a result, it has been found that there exists a distance D at which the phase of the vibration noise signal excited by the second excitation coil 12 and detected by the adjacent detection coil is opposite to that of the noise signal due to eccentricity or vibration excited by the first excitation coil 11 and detected by the detection coil.

[0059] The inventors have confirmed that, for example, when the object to be inspected 3 is a metallic round bar material, and the detection coils 10a, 10b and the first excitation coil 11 and second excitation coil 12 are through coils, there is an optimal value for the distance D between the detection coil and the excitation coil arranged adjacent to it, depending on the difference between the outer diameter of the round bar material and the inner diameter of the coils.

[0060] In the first embodiment of the present invention, a distance D is obtained between the second excitation coil and the adjacent detection coil at which noise signals due to eccentricity or vibration are in opposite phase. The detection coils 10a, 10b, the first excitation coil 11, and the second excitation coil 12 are arranged in the eddy current flaw detection probe 1 so that the distance D between the coil part 12a of the second excitation coil 12 and the detection coil 10a and the distance D between the coil part 12b of the second excitation coil 12 and the detection coil 10b are the same. This makes it possible to eliminate noise due to eccentricity or vibration even when vibration of the eddy current flaw detection probe 1 of the eddy current flaw detection device 100 or eccentricity of the test object 3 occurs.

[0061] By optimally setting the distance D between the second excitation coil and the detection coil, the vibration noise signal excited by the second excitation coil and detected by the adjacent detection coil will be in opposite phase to the vibration noise signal excited by the first excitation coil and detected by the detection coil, i.e. the phase will be shifted by 180 degrees. As a result, the composite signal of the excitation coil and detection coil generated by noise due to eccentricity or vibration can be attenuated.

[0062] It was also confirmed that the eddy current signal due to scratches or the like on the test object 3 does not change with respect to the eddy current due to the detection coil and the excitation coil located next to it. As a result, noise due to eccentricity or vibration can be eliminated, and the S / N ratio can be improved.

[0063] Next, a specific example of the present invention will be described with reference to Fig. 4. In this specific example, a round bar is made eccentric, and impedance changes are detected by a detection coil, and it has been confirmed that noise signals due to vibration or eccentricity of the test object can be eliminated.

[0064] FIG. 4 is a schematic diagram for explaining a specific example in which the removal of noise due to vibration of the eddy current flaw detector according to the present invention and eccentricity or vibration of the test object has been confirmed.

[0065] 4, the eddy current flaw detection probe 1 includes detection coils 10a, 10b and a pair of coil portions 11a, 11b constituting a first excitation coil 11 so as to sandwich the detection coils 10a, 10b. A pair of coil portions 12a, 12b constituting a second excitation coil 12 is provided so as to sandwich the pair of coil portions 11a, 11b.

[0066] The inner diameters of the detection coils 10a and 10b are the same as those of the coil portions 11a and 11b of the first exciting coil 11 and the coil portions 12a and 12b of the second exciting coil 12. An object to be inspected 3 made of a metal round bar is inserted into these coils.

[0067] As shown in FIG. 4, the object under test 3 was tilted and moved in the direction of the arrow in the figure by a moving distance d of the end portion, centered on the center (c) in the radial and longitudinal directions between the detection coils 10a, 10b.

[0068] AC power is applied to the coil portions 11a and 11b of the first excitation coil 11 and the coil portions 12a and 12b of the second excitation coil 12. The change in impedance is detected by the detection coils 10a and 10b. The AC power to the coil portions 11a and 11b of the first excitation coil 11 and the coil portions 12a and 12b of the second excitation coil 12 is controlled so that there are two cases: when AC power is applied only to the first excitation coil 11, and when AC power is applied only to the second excitation coil 12.

[0069] The present inventors have confirmed that the detection result of excitation of only the first excitation coil 11 and the detection result of excitation of only the second excitation coil 12 have different phases.

[0070] Next, since the phases of the detection signals calculated from the composite signal of the detection values ​​obtained by exciting the first excitation coil 11 and the second excitation coil 12 are different, it can be seen that noise due to eccentricity or vibration is offset and the noise can be reduced.

[0071] It is considered that there is a distance D between the second excitation coil and the detection coil where the phases of the two detection signals are almost opposite, that is, the phases of the two are approximately 180 degrees. By setting the distance D between the excitation coil and the detection coil to this distance where the phases are opposite, it is possible to cancel out noise caused by eccentricity or vibration and eliminate the noise.

[0072] In this way, according to the present invention, by setting the distance D between the excitation coil and the detection coil to a distance that results in opposite phases, noise due to eccentricity or vibration can be eliminated, and the S / N ratio can be improved.

[0073] In the first embodiment described above, in order to reliably eliminate noise due to eccentricity or vibration, the distance D between the excitation coil and the detection coil is set so that the two detection signals have opposite phases.

[0074] Next, a second embodiment of the present invention will be described with reference to Fig. 5 to Fig. 7. Fig. 5 is a schematic diagram of an eddy current flaw detector and an object to be inspected according to the second embodiment of the present invention, Fig. 6 is a schematic circuit diagram showing the configuration of the eddy current flaw detector according to the second embodiment of the present invention, and Fig. 7 is a block diagram showing the eddy current flaw detector according to the second embodiment of the present invention. Note that the second embodiment is the same as the first embodiment except for the configuration of the second excitation coil, so the same parts are denoted by the same reference numerals and description thereof will be omitted.

[0075] The eddy current inspection probe 1 used in the eddy current inspection device according to the second embodiment of the present invention is formed in a cylindrical or semi-cylindrical shape, and includes a pair of detection coils 10a, 10b, a first excitation coil 110 that generates an excitation magnetic field to generate an eddy current in the surface layer of the inspection object 3, and a second excitation coil 12. The second excitation coil 12 is composed of a pair of coil parts 12a, 12b that are arranged coaxially with the detection coils 10a, 10b so as to sandwich the pair of detection coils 10a, 10b. The eddy current inspection probe 1 according to the second embodiment of the present invention is a probe used in a mutual induction type eddy current inspection device. The first excitation coil 110 is used as a mutual induction excitation coil. The second excitation coil 12 is used as a noise cancellation excitation coil.

[0076] The first excitation coil 11 in the first embodiment is composed of a pair of coil parts 11a, 11b arranged coaxially so as to sandwich the pair of detection coils 10a, 10b, whereas the first excitation coil 110 in the second embodiment is arranged concentrically with the detection coils 10a, 10b. In this manner, by arranging the first excitation coil 110 concentrically with the detection coils 10a, 10b, the length of the eddy current flaw detection probe 1 can be made shorter than that of the probe in the first embodiment.

[0077] Fig. 6 is a schematic circuit diagram showing the configuration of the detection coil portion of the eddy current flaw detector according to the present invention. As shown in Fig. 6, a bridge circuit 24 is composed of detection coils 10a and 10b and resistors 13a and 13b. The detection coils 10a and 10b are connected as two sides of the bridge circuit 24, and the resistors 13a and 13b are connected as the other two sides of the bridge circuit 24.

[0078] A first excitation coil 110 is provided so as to cover the detection coils 10a and 10b. A second excitation coil 12 consisting of a pair of coil portions 12a and 12b is provided so as to sandwich the detection coils 10a and 10b. This embodiment is a mutual induction type eddy current flaw detector in which excitation is performed by the first excitation coil 11 and detection is performed by the detection coils 10a and 10b. Other than the configuration of the first excitation coil 110, the configuration is the same as that of the first embodiment.

[0079] Next, an eddy current flaw detector according to a second embodiment of the present invention will be further described with reference to the block diagram of FIG.

[0080] As shown in FIG. 7, the eddy current flaw detector 100 includes an oscillator 21, a first power amplifier 22, a second power amplifier 23, a bridge circuit 24, a detection phase converter 26, an amplifier 25, and a phase detector 27.

[0081] As shown in FIG. 6, the bridge circuit 24 is composed of the detection coils 10a and 10b of the eddy current flaw detection probe 1 and resistors 13a and 13b.

[0082] The AC output from the oscillator 21 is amplified by a first power amplifier 22 and provided to a first excitation coil 110. In addition, the AC output from the oscillator 21 is amplified by a second power amplifier 23 and provided to coil sections (noise cancellation coil sections) 12a and 12b of the second excitation coil 12.

[0083] The object under test 3 is excited by AC outputs applied to the first excitation coil 110 and the coil portion 12a and coil portion 12b of the second excitation coil 12. Then, the detection coils 10a and 10b detect impedance changes accompanying changes in magnetic flux generated by eddy currents.

[0084] An unbalanced output between the detection coils 10a, 10b output from the bridge circuit 24 is amplified by an amplifier 25 and sent to a phase detector 27. An AC output from the oscillator 21 is applied to a detection phase converter 26. An output of the detection phase converter 26 is applied to the phase detector 27.

[0085] The detection phase converter 26 converts the signal from the oscillator 21 into a signal having the same phase as the excitation signal and a signal having a phase shift of 90 degrees with respect to the excitation signal, and supplies the converted signal to a phase detector 27 .

[0086] The unbalanced output amplified by the amplifier 25 and the output of the detection phase converter 26 are applied to a phase detector 27, and the outputs of the detection coils 10a, 10b are detected together with the output of the detection phase converter 26.

[0087] In this embodiment, damage or the like of the object under test 3 is detected based on the output values ​​from the detection coils 10a and 10b.

[0088] Next, an eddy current flaw detector according to a third embodiment of the present invention will be described with reference to the block diagram of FIG. In the third embodiment shown in Fig. 8, the distance D between the second excitation coil and the detection coil is set to a predetermined value, and if the detection signals are not in opposite phase, the phase of the signal provided to the second excitation coil is converted and adjusted so that the signals are in opposite phase. For this reason, in the third embodiment shown in Fig. 8, the AC output from the oscillator 21 is provided to a second excitation phase converter 40. Note that the third embodiment shown in Fig. 8 is the same as the first embodiment except for the provision of the second excitation phase converter 40, and therefore the same parts are denoted by the same reference numerals and description thereof will be omitted.

[0089] As shown in Fig. 8, the AC output from the oscillator 21 is provided to a second excitation phase converter 40. This second excitation phase converter 40 converts the phase of the excitation AC power provided to the coil portions 12a and 12b of the second excitation coil 12. This second excitation phase converter 40 converts the phase of the AC power provided to the coil portions 12a and 12b of the second excitation coil 12 so that the phases of both detection signals become opposite to each other.

[0090] The AC power phase-converted by the second excitation phase converter 40 is applied to the second power amplifier 23 , where it is amplified, and applied to the coil portions 12 a and 12 b of the second excitation coil 12 .

[0091] As a result, the coil portions 12a and 12b constituting the second excitation coil 12 are excited by being supplied with AC power phase-converted by the second excitation phase converter 40, and the detection signals from the detection coils 10a and 10b and the detection signals from the detection coils 10a and 10b are excited by being supplied with AC power to the coil portions 11a and 11b of the first excitation coil 11, so that the phase signals are in opposite phase, thereby improving the S / N ratio.

[0092] In the above-described embodiment, a case has been described in which a through coil is used, but the present invention can be applied not only to through coils, but also to internally inserted coils and upper coils, and similar effects can be obtained.

[0093] In the above-mentioned embodiment, the case where the object to be inspected is a metal round pipe material or a metal round bar material has been described, but the object to be inspected is not limited to a metal round pipe material or a metal round bar material, and can also be a metal square pipe material or a metal square column material. In this case, the eddy current flaw detection probe may be formed in a rectangular pipe shape formed so as to surround the object to be inspected, or in a rectangular plate shape arranged at a distance from the surface of the object to be inspected. [Explanation of symbols]

[0094] 1: Eddy current testing probe 3: Test object 10a: Detection coil 10b: Detection coil 11: First exciting coil 12: Second exciting coil 21: Oscillator 22: First power amplifier 23: Second power amplifier 24: Bridge circuit 25: Amplifier 26: Phase converter for detection 27: Phase detector 28: Signal processing device 29: Output section 30: AC power supply 31: Detection unit 40: Second excitation phase converter 100: Eddy current flaw detection device

Claims

1. An eddy current flaw detector comprising a pair of detection coils arranged coaxially and spaced apart from each other in a non-contact manner with respect to an object to be inspected, and a bridge circuit in which two sides of a bridge are formed by the detection coils so that magnetic fields generated by the detection coils are in opposite phases, a first excitation coil that generates an excitation magnetic field to generate an eddy current in a surface layer portion of the object to be inspected; a second excitation coil configured with a pair of coil sections arranged coaxially with the pair of detection coils so as to sandwich the pair of detection coils, the second excitation coil generating an excitation magnetic field to generate an eddy current in a surface layer portion of the object to be inspected; An eddy current flaw detection device, wherein the distance between the detection coil and the coil portion of the second excitation coil arranged adjacent to it is set to a distance at which a phase change occurs between a noise signal due to eccentricity or vibration excited by the second excitation coil and detected by the adjacent detection coil, and a noise signal due to eccentricity or vibration excited by the first excitation coil and detected by the detection coil.

2. The eddy current flaw detector according to claim 1, An eddy current flaw detection device, wherein the first excitation coil is composed of a pair of coil sections arranged coaxially with each of the pair of detection coils so as to sandwich the pair of detection coils, and the coil sections of the first excitation coil are arranged between the detection coil and each coil section of the second excitation coil.

3. The eddy current flaw detector according to claim 1, An eddy current flaw detection device, wherein the first excitation coil is arranged concentrically with the detection coil and on the outer circumferential side of the detection coil.

4. The eddy current flaw detector according to any one of claims 1 to 3, An eddy current flaw detection device, wherein the distance between the detection coil and the second excitation coil arranged adjacent to it is set to a distance such that a noise signal due to eccentricity or vibration excited by the second excitation coil and detected by the detection coil arranged adjacent to it has an opposite phase to a noise signal due to eccentricity or vibration excited by the first excitation coil and detected by the detection coil.

5. The eddy current flaw detector according to any one of claims 1 to 4, an eddy current flaw detection device which converts the phase of the AC power to be provided to the second excitation coil so that a noise signal due to eccentricity or vibration that is excited by the second excitation coil and detected by the detection coil located adjacent to the second excitation coil and a noise signal due to eccentricity or vibration that is excited by the first excitation coil and detected by the detection coil by providing AC power to the first excitation coil are in opposite phase to each other.

6. The eddy current flaw detector according to any one of claims 1 to 5, a first power amplifier that amplifies an AC output from the oscillator; a second excitation phase converter that converts a phase of the AC output from the oscillator; and a second power amplifier that amplifies the AC output from the second excitation phase converter, an eddy current flaw detector that applies AC power from the first power amplifier to the first excitation coil, and applies AC power from the second power amplifier to the second excitation coil.

7. The eddy current flaw detector according to any one of claims 1 to 6, the test object is a metal round bar material or a metal round pipe material, the detection coil, the first excitation coil, and the second excitation coil are through coils, and a distance between the detection coil and the second excitation coil is set based on a difference between an outer diameter of the metal round bar material or the metal round pipe material and an inner diameter of the detection coil and the second excitation coil; Eddy current flaw detection equipment.

8. The eddy current flaw detector according to any one of claims 1 to 6, the test object is a metal round pipe material or a metal round bar material, an eddy current flaw detection probe disposed adjacent to the object to be inspected and having the detection coil, the first excitation coil, and the second excitation coil; The eddy current testing apparatus, wherein the eddy current testing probe is formed in a cylindrical or semi-cylindrical shape.

9. The eddy current flaw detector according to any one of claims 1 to 6, The test piece is a metal square pipe material or a metal square bar material, an eddy current flaw detection probe disposed adjacent to the object to be inspected and having the detection coil, the first excitation coil, and the second excitation coil; An eddy current flaw detection device, wherein the eddy current flaw detection probe is formed in a rectangular pipe shape formed to surround the object to be inspected or in a rectangular plate shape arranged at a distance from the surface of the object to be inspected.

Images